The short-term safety and efficacy of bariatric surgery for the initial remission of type 2 diabetes in moderate to severe obesity is established. However, there are no prospective randomized controlled trials (RCTs) that have tested long-term efficacy and durability. In this context, four investigative groups (Cleveland Clinic, Joslin Diabetes Center Boston, the University of Pittsburgh, and the University of Washington) have completed RCTs that evaluated the short-term (1-3 years) effectiveness of bariatric surgery compared to multidisciplinary medical and lifestyle management of diabetes and body weight. Investigators from these four RCTs have now formed the Alliance of Randomized Trials of Medicine versus Metabolic Surgery in Type 2 Diabetes (ARMMS- T2D) Consortium and prepared this U34 application with the intent of developing a cohesive U01 application to support the long-term follow-up of 302 patients with diabetes who were randomized to surgical or non-surgical diabetes management approaches. These RCTs include a set of common measures, and all have completed at least one-year follow-up assessments. Through the U34 mechanism, we will merge study participants and harmonize study procedures and outcome metrics into a unified, prospective, longitudinal, observational framework. The primary aim of the subsequent U01 will be to determine long-term (7 years) efficacy and durability of glycemic control (HbA1c =6.5%, without diabetes medications) following random treatment allocation to bariatric surgery or medical/lifestyle intervention. Secondary outcomes include, HbA1c =6.5% on medications (e.g. metformin), body weight, dyslipidemia, hypertension, hypoglycemia, microalbuminuria, major cardiovascular events, quality-of-life, and complications of surgical and medical therapy. In exploratory analyses, we will identify clinical predictors of diabetes remissio and relapse. Our cohorts will form the first RCT to address these questions and represent a cost effective way to generate the data. ARMMS-T2D is expected to have high impact because it will provide the largest body of long-term Level-1 evidence to inform decision-making regarding comparative efficacy, durability, and safety, of bariatric surgery relative to medical/lifestyle management of diabetes among patients with moderate to severe obesity.